Cryptography Introduction

Hash (fingerprint, digest): evenly and randomly maps variable length data
into a smaller fixed size such that it's "one-way" (hard to find a data
object for a given hash result) and "collision-free" (hard to find two data
objects with the same hash result).

Secret Key Cryptography (symmetric): the key used for processing is kept
as a secret between the parties.

Public Key Cryptography (asymmetric): a private/public key pair (inverse
of each other) are used to sign (via the private key) and encrypt (via the
public key).

Signature: a private key is applied to some data (or its hash)

authenticity (a specific key was used),

integrity (the document has been changed),

and non-repudiation (possessor of the key can not deny it was
used.)

Encryption: One often uses a public key (easy to obtain) to send a
symmetric key (efficient) for a "session" of communication.

Key Management: How to obtain the real key of the person with
whom you want to communicate. This typically involves chains of signatures on
a key that must be checked/validated.